1. Field of the Invention
The present invention relates to a motion compensation device which detects vibration of an optical system caused by hand tremors and other sources of undesired vibration. In particular, the present invention relates to a device which can discriminate between undesired movement or vibration of photographic equipment and intentional movement of the photographic equipment and compensate for the undesired movement while not compensating for the desired movement.
2. Description of the Related Art
Optical systems project an image onto an image plane. Conventional image blur suppression device suppress, or reduce, blurring of the image. A motion compensation device is a type of image blur suppression device, and compensates for motion incident upon the optical system. Motion is typically imparted to the optical system by vibrations in the optical system, or in a surrounding holding member. In general, conventional motion compensation devices cause a compensation lens to shift counter to the motion of the optical system so as to shift the image projected by the optical system relative to the optical system. Conventional cameras use a motion compensation device to suppress image blur resulting from motion of the camera. Such motion is typically caused by hand tremors of the photographer.
A motion compensation in the prior art has a structure as disclosed in Japanese Laid-Open Patent Publication JP-A-4-76525 In FIG. 3 of JP-A-4-76525, the overall structure of a prior art optical system which performs motion compensation is shown. A camera having the motion compensation capability of JP-A-4-76525 is equipped with a blurring motion compensation lens which is capable of parallel motion in a plane at right angles to the optical axis. A drive actuator is used to drive the blurring motion compensation lens in up and down, and left and right directions. This drive actuator includes: a lens frame member which supports the blurring motion compensation lens; a plate member which supports this lens frame member; four wires mounted on the plate member; a body which supports these wires; a wound coil; a yoke; and a permanent magnet. A position detection device is included in the drive actuator and detects the position of the blurring motion compensation lens. This position detection device includes a light generating element and a light receiving element.
The operation of the prior art motion compensation devices will be described below with reference to FIG. 8.
FIG. 8 is a block diagram of a prior art blurring motion compensation device.
In FIG. 8 an angular velocity sensor 10 would include a piezoelectric vibration type of angular velocity sensor used to detect a Coriolis force, and is a sensor to monitor the vibration of the camera. The output signal of the angular velocity sensor 10 is input to an integration unit 40 which integrates this output signal over time. After the integration unit 40 has converted the output signal of the angular velocity sensor 10 into a blurring motion angle of the camera, this angle is converted into target drive information for the blurring motion detection lens. A servo circuit 100 is used to drive the blurring motion compensation lens according to the target drive position information. The servo circuit 100 calculates the difference in the target drive position information and the position information of the blurring motion compensation lens, and outputs a signal to an actuator 110. The actuator 110, based on this signal, drives the blurring motion compensation lens within a plane at right angles to the optical axis. A position detection device 120 monitors the movement of the blurring motion compensation lens and feeds it back to the servo circuit 100.
In the prior art of motion compensation devices, once the integration unit 40 integrates the output signal of the angular velocity sensor 10, the information is converted into angular displacement information. As a result of this conversion, when the integration unit integrates the output signal of the angular velocity sensor 10 over time, it is necessary to set a constant of integration (referred to as a "standard value" hereinafter) including the target value of control. The output signal (referred to as "omega zero" hereinafter) of the angular velocity sensor, when the camera is stationary, is generally used as this standard value. This method of calculating the standard value is shown in FIG. 17 and FIG. 18 of Japanese Laid-Open Patent Publication JP-A-4-211230.
The blurring motion sensor of the motion compensation device disclosed in JP-A-4-211230 is equipped with an angular velocity sensor which detects Coriolis force. A drift component detection unit which includes a central processing unit ("CPU") and a memory, calculates the average value of the output signal of the angular velocity sensor sampled in an interval from the present time to a predetermined earlier time. By subtracting the average value of the output signal of the angular velocity sensor the drift component detection unit eliminates the drift portion of the motion detected and outputs this subtraction value.
Output signals of the angular velocity sensor are input every 10 ms into the drift component detection unit. Thereby fifty output signals are input every 0.5 second (10 ms.times.50). The calculated average value (referred to as "average 1" hereinafter) of these fifty output signals is stored in the memory of the drift component detection unit. After ten seconds (0.5 seconds.times.20) has elapsed, the average 1 of a further 20 samples is input. Accordingly, after ten seconds have elapsed from the start, the average can be calculated of 1,000 (50.times.20) output signals of the angular velocity sensor.
In the motion compensation devices of the prior art a problem is encountered when a large and usually intentional movement is detected. These large movements are usually a result of the camera operator changing the composition of the photograph by panning the camera to follow a moving subject or to focus on another subject (referred to as "field of view angle changes" hereafter). As far as the motion compensation device is concerned, these field of view angle changes are random and cannot be distinguished easily from other sources of vibration. The motion compensation device driving the blurring motion compensation lens in an attempt to compensate for these field of view angle changes runs into the movement limits (referred to as "drive limits" hereafter) of the blurring motion compensation lens which distorts the photograph taken and possibly damages the motion compensation device.
FIG. 9A and FIG. 9B are diagrams depicting examples of the output signal of an angular velocity sensor and the resulting drive amount of the blurring motion compensation lens over a period of time when photographic composition changes occur.
Referring to FIG. 9A, when the camera is completely stationary the angular velocity detected is 0 deg/s. As shown in FIG. 9A, the output signal suddenly rises when there is a change in the picture composition. Prior to this sudden change in photographic composition, the camera is approximately stationary in position. The camera is not completely stationary due to the addition of undesired motion such as hand tremors which must be accounted for in this example. For the sake of simplicity, these operator hand tremors are drawn as a sine wave.
FIG. 9B shows the drive amount of the blurring motion compensation lens resulting from the angular velocity sensor of FIG. 9A integrating the output signal as the target value equal to 0. The blurring motion compensation lens, as shown in FIG. 9B, moves in unison with the output signal shown in FIG. 9A. However, as shown by the broken line in FIG. 9B, there exists a drive limitation for the blurring motion compensation lens. Due to this drive limitation, when a large movement of the camera occurs due to a photographic composition change and other causes, the blurring motion compensation lens reaches the drive (movement) limit, and cannot be driven beyond this point. As a result, a vibration motion cannot be compensated for using the blurring motion compensation lens.
In addition, the time interval from t1 to t2 shown in FIG. 9B is the period of initiation of a photographic change, and because the blurring motion compensation lens is in a region within the drive limits, vibration motion can be compensated using the blurring motion compensation lens. However, from the point of view of the camera operator, a very disconcerting phenomena is seen through the viewfinder of the camera. When the camera operator starts panning the camera and causes a field of view change, the motion compensation device compensates for the movement and the image the operator sees does not move in spite of the operator's intentional movement of the camera. Then once the drive limit of the blurring motion compensation lens is reached the image seen by the operator and recorded by the camera suddenly jumps making for a very unnatural view and recording of images by the camera. Because of this phenomena, compensating for vibration motion while making field of view angle changes, it becomes necessary to be able to identify when large movements take place. Japanese Laid-Open Patent Publications JP-A-5-142614 and JP-A-7-261234, provide a method of detecting such large movements due to a field of view angle changes.
FIG. 10A and FIG. 10B are diagrams showing an example of the movement amount of the blurring motion compensation lens and the output signal of the angular velocity sensor when panning. FIG. 10A is a diagram showing the output signal of the angular velocity sensor, and FIG. 10B is a diagram showing the movement amount of the blurring motion compensation lens. In the detection method described in JP-A-5-142614 and JP-A-7-261234, when the output of the detector for a predetermined time is in a fixed direction, it was determined that there is a field of view angle change. As a result, using this detection method as shown in FIG. 10A, when the camera is panned in one direction for a given amount of time, it would be determined that the field of view angle changed.
FIGS. 11A and 11B shows an example of the movement amount of the blurring motion compensation lens and the output signal of the angular velocity sensor when following a subject. FIG. 11A shows the output signal of the angular velocity sensor, and FIG. 11B shows the movement amount of the blurring motion compensation lens.
FIG. 11A shows the output signal of the angular velocity sensor when following the movement of a subject, such as a soccer player, in which random movements occur frequently. As shown in FIG. 11A, the output signal of the angular velocity sensor, as shown in FIG. 10A, does not move in one direction only, but a large output signal is generated in both directions. As a result, using the detection method described in JP-A-5-142614, it cannot be determined that there w as a change in field of view angle.
In this manner, in the prior art motion compensation devices, because there was no way of determining when the operator would intentionally move the camera, the problem arises that vibration motion compensation cannot be performed. In addition, in the prior art vibration motion compensation devices, the problem exists that the image seen in the viewfinder is unnatural. Also, as described in JP-A-5-142614, in the case that the output signal is in a fixed direction for a predetermined time, the vibration detection method would determine that a large movement in the camera is occurring and it could not handle movement of a randomly moving body.
Therefore, it is recognized in the field of photography and optical imaging that a vibration motion detection device is needed which can compensate for undesired vibration with a high degree of precision and naturally track objects when large random movements due to field of view angle changes occur.